The work, as detailed in this proposal, has focused on the mechanism(s) of protection that IL-11 and IL-6 confers in the setting of hyperoxic lung injury. We compared the susceptibility to 100% oxygen of transgenic mice in which IL-11 or IL-6 is overexpressed in an airway-specific fashion and transgene (-) littermates. These studies demonstrated that both IL-11 and IL-6 significantly ameliorates hyperoxia-induced injury. Transgene (+) animals live significantly longer in 100% oxygen and this protective effect is associated with diminished ultrastructural evidence of endothelial injury, alveolar protein leak and lipid peroxidation, while alterations in antioxidants are not of a magnitude to explain this effect. The protective effects of these cytokines are associated with a significant decrease in hyperoxia-induced cell death and DNA fragmentation and the enhanced expression of the Bcl-2 proteins. These studies lead us to hypothesize that IL-11 and IL-6 are protective in the setting of hyperoxic lung injury and this protection is mediated, in part by the inhibition of cell death pathways. To test this hypothesis, we propose to: Aim 1: Characterize the signal transduction pathways that mediate IL-11 and IL-6 induced protection from oxidant stress in vitro and examine the relationship to upregulation of mediators of cell death. We will characterize the contributions of the known components of the IL-11 and IL-6 receptors (IL-11Ra, IL-6R, and gp 130) as well as four different but interacting signaling pathways (JAK/STAT; ras/ERK; rac/JNK, and p38) to the induction of protective effects on cultured human pulmonary epithelial and microvascular endothelial cells incubated in the presence and absence of oxidant stress. Aim 2: Evaluate the contribution(s) of Bcl 2 family proteins to protection of pulmonary epithelial and microvascular endothelial cells in vitro. We will characterize the effects of Bcl 2 family proteins (Bcl-2, Bcl-x, and Bax) by taking advantage of our ability to: (a) transfect and overexpress many of these moieties in primary human cells; (b) use anti-sense approaches to prevent the induction of potential apoptosis regulators in human pulmonary epithelial and microvascular endothelial cells incubated in the presence and absence of oxidant stress; (c) transfect and overexpress many of these moieties in vivo. Aim 3: Evaluate the contribution(s) of Bcl 2 family proteins to protection in vivo. Our studies and those in the literature suggest that the protective effects of IL-6 type cytokines are mediated, at least in part, by their ability to augment the production of specific Bcl-2 family members. We will test this hypothesis by characterizing the effects of IL-11 and IL-6 on the levels of these proteins and the mRNA that encode them and generating and characterizing the sensitivity to 100% O2 of mice that overexpress these moieties.